I'm pretty sure when it asks for [role] it's actually seeking a [role] of a specific level to build a party for whoever is at the front of the "queued for a specific dungeon" line. So if that party needs a tank for the Lv79 dungeon, tank will stay in need until a Lv79 tank joins the queue - and if ten lower-level tanks and zero healers join the roulette queue in the meanwhile, they're waiting on a healer to be partnered with, but tank is still "in need" for a different reason entirely. As soon as a healer joins the roulette, they'd be paired with one of those waiting tanks immediately.
